This project is concerned with the metabolic regulation and mechanism of catalysts of the important biosynthetic enzyme phosphoribosylpyrophosphate (PRPP) synthetase from Salmonella typhimurium. Purification and physical characterization of the enzyme has permitted studies of the functional groups involved in catalysis. The roles of divalent cations and ligand binding in catalysis and allosteric regulation will be investigated. Studies of the unusual asymmetric pentameric subunit structure of the enzyme will be extended. Regulation and metabolic functioning of PRPP synthetase in vivo will be further studied by measurements of changes in PRPP pools in whole cells under various growth conditions and in mutant strains. Searches for a mutant strain defective in PRPP synthetase are proposed. This work provides valuable information for research in human metabolic diseases involving purine and pyrimidine metabolism.